As polymer technology has progressed, the necessity to tailor properties of polymeric materials for particular end uses has increased. Such challenges have been met by using additives which enhance particular properties of the polymer without adversely affecting its other properties. Another approach is to combine various polymers to achieve a balance of properties which are exhibited differently by the parent polymers. Advantages gained by such blends may relate to processing, for example polymer rheology, or to the final blend performance such as in adhesion or toughness.
Most polymer blend combinations, however, have poor mechanical compatibility and in such cases the blends actually sacrifice mechanical advantages which are exhibited by each of the parent polymers. Tradeoffs are sometimes acceptable in order to achieve the desired balance for a particular use. Rarely do polymers combine in admixture to achieve properties which are actually superior in any way to those of the parent polymers making up the blend. The reason for this is that unless the polymers are very similar to one another in structure or exhibit specific interactions, they either will be incompatible and tend to separate over time or interfere with each other's performance and cause an unacceptable degradation in one or more of the properties which are desired.
Olabisi, et. al., Polymer-Polymer Miscibility, pages 238-9, Academic Press, NY (1979), presents a survey of miscible polymer systems which include poly(vinyl acetate) and vinyl acetate copolymers, such as a blend of poly(vinyl acetate) and poly(vinylidene fluoride) and a blend of poly(vinyl acetate) and poly(vinyl nitrate). Other combinations exhibited less homogeneity. Miscible systems involving polyesters and polycarbonates are also discussed, but there is no suggestion to combine poly(vinyl acetate) with poly(propylene carbonate).
U.S. Pat. No. 4,608,417, Giles, (1986), describes overcoming the problem of incompatibility of aromatic polycarbonates with olefin-containing polymers in multilayer compositions by using a tie layer formed by mixing an olefin acrylate with poly(4-methyl-pentene-1). There is no suggestion of blends involving either poly(vinyl acetate) or poly(propylene carbonate).
U.S. Pat. No. 4,698,390, Robeson, et al., (1987), describes a compatible blend of a vinyl chloride derived polymer and a polycarbonate having repeating units derived from bis-(3,5-dimethyl-4-hydroxyphenyl)sulfone. The vinyl chloride polymer can be a copolymer of at least 50 weight percent vinyl chloride and vinyl acetate. The polycarbonates disclosed are quite different from poly(propylene carbonate) and do not suggest blends of such polymers with poly(vinyl acetate).
Rodriguez, F., Principles of Polymer Systems p. 98-101, 403-405, McGraw-Hill, NY (1970), describes bulk and solution polymerization procedures in general and specifically discusses emulsion polymerization for poly(vinyl acetate).
Saunders, K. J. "Poly(vinyl acetate) and Related Polymers", Organic Polymer Chemistry, pages 104-115, Chapman and Hall, London, (1973), describes several different routes for preparing vinyl acetate monomer and discusses emulsion polymerization techniques for production of poly(vinyl acetate). The properties, applications in films and solubilities of the polymer are disclosed. Copolymers of vinyl acetate with alkyl acrylates, fumarates and maleates are described, as in the conversion of poly(vinyl acetate) to poly(vinyl alcohol) and poly(vinyl acetals). Uses of external plasticizers such as dibutyl phthalate is mentioned but there is no suggestion of blends with other polymers.
Rokicki and Kuran, "The Application of Carbon Dioxide as a Direct Material for Polymer Syntheses in Polymerization and Polycondensation Reactions", J. Macromol. Sci.-Rev. Macromol. Chem. C 21 (1), pages 135-186 (1981), cites the work of Inoue et al., as reported in 1969 on synthesis of poly(propylene carbonate) from carbon dioxide and propylene oxide, and further describes other polymerization and polycondensation reactions involving carbon dioxide, such as the copolymerization of carbon dioxide with alicyclic epoxides, e.g. epoxycyclohexane, using diethylzinc-based catalysts. A survey of operable catalysts is included and complete polymerization conditions are described. Properties of carbon dioxide copolymers are discussed and their solubilities in various solvents are contrasted to the insolubilities of polycarbonates from diepoxides. Blends with other types of polymers are not suggested.